This invention relates to a recording/reproducing apparatus which may be used in, for example, a digital video tape recorder or a digital video camera.
There has hitherto been known a digital video tape recorder in which the frequency of vertical synchronization signals in the picture signals supplied from outside, such as component or composite signals, is detected and the number of revolutions of the rotary head is controlled depending on the detected frequency of the vertical synchronization signals for digital recording and analog reproduction of the picture signals.
Such digital video tape recorder is made up of an input/output processing section, a companding section, a recording/reproducing section and a controller for generating clocks of different frequencies and supplying the generated clocks to the respective sections.
Specifically, when recording the picture signals, the controller detects the vertical synchronization signals of the picture signals supplied from outside and, based upon the detected vertical synchronization signals, generates clocks of, for example, 13.5 Mhz, 18MHz and 43 Mhz. The controller routes the 13.5 Mhz clocks to the input/output section, while routing the 18 MHz clocks and the 43 MHz clocks to the companding section and the recording/reproducing section, respectively.
The input/output section converts the picture signals supplied from the outside source into corresponding digital signals, based upon the 13.5 MHz clocks, to generate picture data and generate luminance data and chroma data from the generated picture data, and transmits the luminance and chroma data to the companding unit.
The companding unit divides the luminance and chroma data into blocks, each having a pre-set number of pixels, based upon the 18 MHz clocks, and performs orthogonal transform on the block basis for carrying out the data compression. Picture data for one picture are generated from the compressed block-based luminance and chroma data and routed to the recording/reproducing unit.
The recording/reproducing unit encodes the picture data, based upon the 43 MHz clocks, and appends parity data. The resulting data is routed to a recording head as a rotary head.
The number of revolutions of the recording head is changed depending on the frequency of the vertical synchronization signals of the picture signals supplied from outside. The tape running speed, however, is not changed. The recording head is run in rotation with the thus changed number of revolutions for obliquely recording the picture data on a magnetic tape.
If the frequency of the vertical synchronization signals of the picture signals supplied from outside is the standard frequency, the recording tracks formed on the magnetic tape by obliquely recording the picture data thereon are as shown in FIG. 1a.
If the frequency of the vertical synchronization signals of the picture signals supplied from outside is higher than the standard frequency, the recording head is controlled so that its number of revolutions becomes higher than the standard number of revolutions, so that recording tracks TR having a slope more acute than that of the recording tracks TR for the picture signals having the standard frequency vertical synchronization signals are formed on the magnetic tape, as shown in FIG. 1b.
If the frequency of the vertical synchronization signals of the picture signals supplied from outside is lower than the standard frequency, the recording head is controlled so that its number of revolutions becomes lower than the standard number of revolutions, so that recording tracks TR having a slope flatter than that of the recording tracks TR for the picture signals having the standard frequency vertical synchronization signals are formed on the magnetic tape, as shown in FIG. 1c.
When reproducing the picture data, thus digitally recorded on the magnetic tape, the recording/reproducing unit controls the rotation of the playback head, as a rotary head, so that its number of revolutions is equal to the standard number of revolutions. By detecting the timings of Automatic track finding signals (ATF signals) generated on reproduction, and by applying a tracking servo, the playback head may be controlled to be at an on-track position for correctly reproducing the picture data.
When the picture data are reproduced in this manner, the recording/reproducing system performs time base correction and error correction on the reproduced data and routes the resulting data to the companding unit, based upon the 43 MHz clocks.
The companding unit divides the picture data into blocks, each having a pre-set number of pixels, based upon the 18 MHz clocks, and performs inverse orthogonal transform on the blocked data on the block basis, and routes the transformed data to the input/output processing unit.
The input/output processing unit generates picture data for one picture from the picture data, supplied on the block basis, based upon the 13.5 MHz clocks, and separates the picture data into luminance data and chroma data. These luminance data and chroma data are converted into corresponding analog luminance and chroma signals which are outputted via an output terminal to an outside device, such as a monitor device.
Thus the digital video tape recorder is responsive to the frequency of the vertical synchronization signals of the picture signals supplied from outside in order to control the number of revolutions of the recording head and the playback head so that the picture signals supplied from outside may be correctly recorded or reproduced even although the frequency of the vertical synchronization signals of the picture signals supplied from outside is different from the standard frequency.
However, with the above digital Video tape recorder, since the number of revolutions of the recording head is controlled responsive to the frequency of the vertical synchronization signals of the picture signals from the outside source for recording the picture signals, the slope of the recording tracks is more acute than a standard gradient if the frequency of the vertical synchronization signals is higher than a standard frequency, as shown in FIG. 1b, while becoming flatter than the standard gradient if the frequency of the vertical synchronization signals is lower than the standard frequency, as shown in FIG. 1c. The picture data recorded for the standard frequency of the vertical synchronization signals may be correctly reproduced by another digital video tape recorder not having the function of controlling the rotation of the recording/playback head. However, if the rotation of the recording head is controlled, for example, increased, in recording the picture data, the recorded data cannot be reproduced correctly by another digital tape recorder.
The above-described problem of interchangeability between different devices of the same version becomes more outstanding because the gradient of the recording tracks TR becomes more acute or flatter when the number of revolutions of the recording head becomes higher or lower than a standard value, respectively.
Also, with the above-described digital video tape recorder, since the number of revolutions of the recording head is changed depending on the frequency of the vertical synchronization signals, it has been necessary to increase the phase capture range of a phase-locked loop (recording PLL circuit) which is designed to maintain a constant number of revolutions of the recording head during the recording. The result is that the recording PLL circuit becomes unstable after phase capture so that fluctuations tend to be produced even when the frequency of the vertical synchronization signals of the picture signals supplied from out, side is the standard frequency.
On the other hand, since it is necessary to increase the phase capture width of the recording PLL circuit, it is necessary to correspondingly increase the phase capture width of a PLL circuit designed to generate the playback clocks to a value larger than the phase capture width of the recording PLL circuit, with the result that the playback PLL circuit is again lowered in stability after phase capture.